Just dig a two- or three-block-wide hole going down, bridging the area between with wood platforms every time the last one placed has moved off the screen and also a torch if you have them. This is very useful for discovering caves and the Underground Jungle, as well as providing quick access to The Underworld.

The best part is the quick ascent, as you can use momentum if you are quick enough with your clicks, the biggest con is that you need a lot more wood compared to other techniques. This can be avoided by not building wooden platforms. Instead, avoid fall damage by using a Lucky Horseshoe, Wings, or double-jump just before the bottom of your mineshaft with a Cloud in a Bottle, and use a Magic Mirror (to return to base quickly).

For a safe and quick way down to the Underworld, assuming you don't have a Lucky Horseshoe, bring a few buckets and make a two-block-deep pool of water to fall into. This must be placed just above the Underworld however, as water cannot exist in the Underworld.

After completing the excavation or during it, you can build a vertical column with rope in the center of the tunnel from the beginning to the end. In this manner
you may go up and down at the same speed.The rope can be bought from The Merchant.

Pit Bridge Fall is a way to safely make your way down drops without risking pressure plates, lava, etc. When you see an area underground with a drop, dig down to it and make sure you have a 2-block wide floor directly below you. Instead of breaking both of the blocks, break a single one and place a new block underneath the remaining one, then break the block you are standing on. Repeat until you reach the bottom.

If you dig through water and don't have a water accessory/potion you might drown and lose your coins/items. To prevent this and making mining easier consider bringing along some Gills Potion or a Diving Helmet which you can get from Sharks in the Ocean. Furthermore, as torches won't work under water, consider bringing along some Glowsticks, Flare Gun, or some Cursed Torches/ Ichor Torches (if in Hardmode), or you can take the alternative, dig a 1 by 1 hole that isn't in contact with the water blocks, and place a regular, colored or ultra-bright torch.

When you come across water while digging downward, place blocks in the water where you want the walls of your tunnel. Sand, silt or any other gravity affected block can be useful here. Once your tunnel is completely sealed off from the rest of the body of water, you'll need to drain the water inside its walls. If there is a natural cave handy, you can dig an outlet to let the water drain into that. Otherwise, dig a cavity off to the side starting from the bottom of your tunnel, allowing the water to drain into the new reservoir. Seal off the drain and continue on your way. If you are digging sideways you first need to place blocks behind you before digging through the water, to prevent from flooding your tunnel, while the rest is the same as digging downwards.

If you have access to the required Pumps, Wires, and Timers, the process of draining the tunnels can be made much easier. Instead of digging a drain from your new section of tunnel, you can pump the water from it to any nearby cave or reservoir. Simply place an Inlet Pump at the lowest point of your tunnel and wire it to an Outlet Pump where you want the water to end up. Attach a timer to the circuit and watch as your tunnel is automatically drained of water. Reclaim your equipment and continue on your way. The disadvantage of this is that it likely requires more time than the previously mentioned method.

Alternatively to the Pump method and the draining method, if you have access to a Hellforge, place one below the water. Then, place one of the opposite liquids (lava for draining water, water for draining lava), then dig a hole draining the liquid into the hellforge, this, because it is blocking formation of obsidian, deletes the liquids, without missing something OR creating obsidian.

When digging underwater or exploring flooded caves, you may run out of breath far from the surface. To avoid drowning, tunnel into one of the walls a little way then mine the two blocks above your head so that it forms an air pocket. Either jump or grapple up into the bubble to get a breath of fresh air.

No solid blocks can be placed in lava, so digging through lava can be a problem. Also digging in a horizontal direction through lava is not recommended, because it is difficult and expensive. Compared to digging through water consider bringing along a higher tier pickaxe, capable of digging through Obsidian, as well as Obsidian Skin Potions and Sand or Silt. Additionally consider bringing along some Gills Potions.

This works much the same as digging through water. The biggest difference is, of course, the extremely hazardous nature of lava. Sand or silt blocks must be dropped into the lava in order to form the walls of your tunnel. If you want the walls to be made of some other material, drop them an additional block to either side, so you have room to place the permanent walls before reclaiming the temporary ones. It is extremely useful to have Obsidian Skin Potions at this point. You can then jump into the lava-flooded tunnel and drain the lava exactly as you would water (with or without pumps).

If you do not have protection from lava, you will have to tunnel all the way around the lava and dig a reservoir (or locate a natural cave) to drain the lava from your tunnel into. You must be certain that the reservoir is large enough to hold all of the lava, otherwise expanding it may be very time consuming. Finally, connect the reservoir the lowest part of the flooded section so that it drains completely. Be careful doing this so that no lava touches you, of course.

Vertical and diagonal tunnels. Bricks placed for appearance.

A faster way is to dig using water. In this method you flood your tunnel with it, so that it turns lava into Obsidian while mining downward through it. Newly formed Obsidian will become the walls of your tunnel (but can be replaced). Using water you can also dig diagonally downward. As the tunnel is likely to be flooded you may want to use a method for breathing underwater. The Gills Potion is particularly useful because air pockets tend to clutter the tunnel. Water rapidly evaporates (disappears) in the Underworld, so if this method is to work the water must be replaced with honey. This will however produce Crispy Honey Blocks instead of Obsidian.

Digging through the underworld presents unique challenges, particularly in managing the lava spawned when hellstone is mined. When mining hellstone you need the same equipment as mining through lava. You may also want to bring a Bucket with you.

The fastest and easiest method by far is to use Obsidian Skin Potions. That way you don't have to surround the hellstone with blocks or move the lava. Furthermore, you can simply jump in one of the many lava lakes for easy access to the hellstone. This will also prevent most monsters from spawning or reaching you. Do, however, keep an eye on the remaining buff time, as you will die within seconds after it runs out. One could use a Magic Mirror to quickly escape after the buff has disappeared (or immediately before if you notice), granted the player doesn't die of fire damage.

Alternatively, you can surround the hellstone veins completely with a layer of blocks. That way, when the hellstone is mined, the lava it generates will be safely contained. While standing outside the barrier, mine the hellstone vein. Remember that only the items within 3 blocks will be picked up automatically. If some hellstone is out of reach, either drain the lava into a reservoir or use buckets to move it. After ALL of the lava has been relocated, remove the barrier. Create a new barrier against the remaining hellstone like before, then continue mining the vein.

Plus, if you can find some hellstone on the that is not submerged in lava, you can cover it with dirt blocks, mine it, place another layer of dirt blocks where it was and then remove the top layer of dirt.

A another option that is reasonably fast is by exploring the tower-like Ruined Houses in the underworld. There are often Hellstone ore veins next to the towers, and the thin wall of Obsidian Brick between the Hellstone, and this makes a perfect natural barrier. The player can mine most Hellstone ore veins, and if some Hellstone is just out of reach, just mine a single brick and stand back, as the tower makes a perfect natural reservoir. An Extendo Grip can also help with this.

A last option on mining Hellstone is to make a obsidian platform over a dry pit and mine the Hellstone above you. Then have the lava flow into the pit out of harms way. (only works with obsidian platforms because of their ability to not get destroyed by lava and letting the lava fall through them but keeping the items on top for very efficient mining.)

The simplest way to mine Hellstone is to come to the Underworld with a decent amount of Obsidian Skin Potions and swim around the lava lakes, mining Hellstone without the danger of suffering lava damage, or taking damage from the fire properties of the block itself. Furthermore, most enemies won't spawn while you are submerged in lava. As noted above, Hellstone doesn't burn up in lava, so it is perfectly fine if the item isn't picked up immediately by the player. A secondary way to this method is using Lava Waders. The 7 seconds of lava immunity is much longer than you would think if you have a decent pickaxe. You can also mine a tunnel leaving a wall between you and the hellstone and mine it, then guide the lava away from the place you are mining by breaking the blocks next to it mine to where you mined the hellstone and collect it.

If you do not have Obsidian Skin Potions or Lava Waders, a simple alternative is to specifically mine only the blocks you can immediately pick up, so if there's a block of Hellstone two blocks to the right of you, you can mine it.

If the Player places 50 pieces of Meteorite Ore or more on the screen where they are mining, they can create an artificial Meteor Biome. In the Meteor biome, all monster spawns are replaced by Meteor Heads, which are more predictable, and tend to do less damage than the naturally spawning creatures of The Underworld. If the Player can withstand the Meteor Head attacks, they can mine Hellstone in relative peace.

If this method is used, the Player only needs to take care to move the Meteorite deposit as they mine away from it. Refer to the Meteorite page for tips on safely mining in the Meteor biome.

There is a hidden limit to the number of spawned enemies that can be spawned at once. You can use this to your advantage by simply not killing the enemies that are not a threat to you, but keeping them close enough to you that they don't despawn. This functionally prevents any actually threatening enemy from spawning, letting you dig at your own leisure.

The simplest way to accomplish this is to place dirt (or any other block you have in huge quantities) tunnels or dig tunnels in the ash while letting demons and bats fly around you just above. Don't kill them.

If a bone serpent spawns, it will be trouble, but you have time to regenerate once it is dead. If an imp spawns, either destroy its projectiles until it decides to teleport inside your tunnel, and kill it there, or use the Vilethorn to kill it from inside your tunnel.

Keep in mind that creatures need a certain amount of space to spawn - imps take a 2x3 tile area to spawn, and bats take 2x2. If you are worried about spawns in your tunnels, either place dirt/stone walls to prevent that, or else place dirt behind you so that no space larger than 2x2 is remaining.

The trick is to not go so far away that the demons or bats can despawn - it may actually be worthwhile to dig them a separate little access tunnel of their own, as well.

Once your spawn limits are hit, you can dig in peace using the "reservoir" method to find places to put the excess lava.

Using this method requires the most patience, but it can net the most profit, as you can loot basically as much of the Underworld in one go as you can carry.

Another effective method of Hellstone collection is utilizing the naturally spawned structures present in The Underworld. A player may mine Hellstone with little or no danger by mining through Underworld structures' walls in close proximity to Hellstone, being protected from both contact with the Hellstone, and the lava created by the Hellstone.

This method can be expanded upon by making "pockets" in the ash that makes up the Underworld. Ash is very easy to mine, so digging lava pathways from the relative comfort of the Underworld's structures can be very useful by guiding lava in the way of mining to a different spot, allowing you to access the entire deposit with less risk. An Obsidian item is still recommended for this method, and even a Lava Charm for safety, as working directly with Hellstone will always be hazardous. With proper tunnels and platforms, however, you can cut down a lot of risk while getting a larger yield than just the scraps on the sides of structures.

Use your Pwnhammer to destroy at least three Altars. Destroying more Altars increases the amount of hardmode ore, but also increases the risk of spawning hallow/evil in inconvenient locations such as your home. If you decide to pwn all the altars, be sure to craft the Night's Edge first!

Most areas deep enough to spawn hardmode ores have significantly more powerful monsters in hardmode. Exercise caution while exploring new caverns, and avoid especially dangerous areas such as the Jungle.

Consider returning to the Underworld, which is now one of the safest biomes. Its ash ceiling can contain Titanium/Adamantite, and gaps in the ceiling give quick access to many deep caves. You may also have extra opportunities to fight the Wall of Flesh to collect additional drops, and to purify a Tax Collector.

Dart Traps, although the most common type of traps, are somewhat rare. They can be found by using a dangersense potion. Alternatively, holding an electric item(or Mechanical Lens/The Grand Design) and finding horizontal lines of wiring is another idea (if the wire line is vertical it is probably a boulder trap).
If the lines are short and not straight, it may be some explosives, statues or geysers.
The geysers can only be found in lava layer and the statues are often near a chest, that can be detected by Metal Detector or higher.

Upgrade your equipment regularly. Better pickaxes mean faster mining. If you carry a Nightmare Pickaxe/Deathbringer Pickaxe as well as a Molten Pickaxe then you have the ability to dig through dirt, mud, and sand extremely quickly. The Nightmare/Deathbringer Pickaxe should be used on these types of blocks due to its faster swing speed, while still requiring the same amount of hits per block as the Molten Pickaxe. The Molten Pickaxe should be used on all other materials as they take more hits with the Nightmare/Deathbringer Pickaxe. Once you gain even higher tier pickaxes (or drills) this is no longer needed.

Know your goal: Are you mining for stone or ore? Are you trying to find Chests? Having a clear idea of what you are looking for and where that item is mostly found is a good idea. For example, Ice, Slush and Snow are all easily found in the tundra biome, so you would begin mining where it snows.

If you come to a choice between stone or dirt and do not have a Molten Pickaxe, dig through the dirt, as it is faster to dig through with any other pickaxe, while the Molten is the same speed for either.

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